Analysis of optical phase-conjugate characteristics of picosecond four-wave mixing signals in semiconductor optical amplifiers

We have analyzed for the first time the optical phase-conjugate characteris tics of picosecond four-wave mixing (FWM) signals in semiconductor optical amplifiers (SOAs) using the finite-difference beam propagation method (FD-B PM). In this study, we show that the optical phase-conjugate characteristic s of the FWM signals are strongly dependent on input pump pulsewidths. As a typical example, we have demonstrated that SOAs act as an ideal phase-conj ugator, within the confines of reversing the chirp of optical pulses, for a 10-ps input pump pulse and a similar to2.2-ps linearly chirped input probe pulse. When the pulsewidth of pump pulse becomes short, the minimum compre ssed pulsewidth is obtained by using a fiber shorter in length than the inp ut fiber, but having the same group velocity dispersion as the input fiber. For a much shorter pump pulse such as 1 ps, the short FWM signal can be ob tained via the gating characteristics of the FWM. However, only a part of t he phase information is copied to the FWM signal due to such gating charact eristics. The phase information is also degraded due to the fast nonlinear effect in the SOA. Thus, the pulsewidth is not compressed by propagation th rough a dispersive medium.